This invention relates to an organic electro-luminescent, hereinafter referred to EL, element, a material of electro-luminescent element, and an electro-luminescent display apparatus.
Although an inorganic electro-luminescent element have been usually used as a flat panel light source, a high voltage alternating current is necessary to drive such the light emission element.
A recently developed organic electro-luminescent element is constituted by a thin layer containing a fluorescent organic compound provided between a cathode and an anode. The organic electro-luminescent element is an element emitting light, fluorescent or phosphorescent light, generated by deactivation of an exciton which is formed by an electron and a positive hole injected into the thin layer. Such the element is a self-light emission type element which can emit light by a low voltage power source such as several volt to several dozens volt. Accordingly the element is noticed from the viewpoint of space saving and portability since such the element is a thin layer type complete solid element having a wide visible angle and a high visuality.
Although various organic EL elements have been reported, no example has been reported which satisfies the required properties such as the brightness of emitted light and the life regarding the element emitting light within the range of from blue to bluish purple. For example, Japanese Patent Publication Open to Public Inspection hereinafter referred to JP O.P.I., No. 3-152897 reports an organic electro-luminescent element containing p-quaternary phenyl emits light of 420 nm. However, such the element is insufficient in the brightness of emitted light.
Compounds including benzimidazole in the molecular thereof are disclosed in JP O.P.I. Nos. 10-92578 and 10-106749, but the brightness of emitted light is insufficient.
A fluorescent material composed of a pyrazoline compound is disclosed in JP O.P.I. No. 6-184531. However, such the compound is insufficient from the viewpoint of thermal stability for using as the material of the organic EL element.
It is known in JP O.P.I. No. 8-286033 that N,Nxe2x80x2-diphenyl-N,Nxe2x80x2 (3-methylphenyl) [1,1xe2x80x2biphenyl]-4,4xe2x80x2-diamine (TPD) emits light at 420 nm. However, this compound has a shortcoming that the color purity is low when red light is made by the use of a color conversion filter.
As the light emission material for the organic electro-luminescent element emitting light of from blue to bluish purple, a material capable of emitting higher light brightness is demanded from such the viewpoints and further raising in the energy conversion efficiency and the quantum efficiency of light emission are expected.
In an organic EL element emitting light in the region other than blue to bluish purple, a positive hole charge transportation material excellent in the thermal stability is required by which the light emitting layer can emit light with a high brightness.
When an organic EL element or a display device using an organic EL element is used as a portable tool, one using a glass substrate is possibly broken by an accidental shock such as falling since such the device has no flexibility.
The degradation of the light emission property of the organic EL element is caused by formation of a dark spot which is formed by inversion of moisture of the atmosphere.
The first object of the invention is to provide an organic EL element capable of emitting light within the range of from blue to bluish purple and excellent in the light brightness and the life. The second object of the invention is to provide an organic EL element excellent in the brightness of the emitted light and the life. The third object of the invention is to provide an organic EL element capable of emitting light within the range of from blue to bluish purple and excellent in the brightness of the emitted light and the life. The fourth object of the invention is to provide a positive hole charge transportation material for constituting an organic EL element excellent in a long life. The fifth object of the invention is to provide a display apparatus using the organic EL element. The sixth object of the invention is to provide an organic EL element having flexibility. The seventh object of the invention is to provide an organic EL element maintaining stable luminescence property in the atmosphere.
The invention is attained by the find by the inventors that an organic element emitting light within the range of from blue to bluish purple and having excellent brightness of emitted light and life can be obtained by the use of a specific compound.
Moreover, it is found that a compound is suitable, in which the central nitrogen-carbon bond of a triarylamine is twisted by introducing a substituent to the position-2 of the aryl group. In such the case, the light emitting efficiency is raised when a cathode buffer layer is provided between the light emission layer and the cathode.
Furthermore, the light emitting efficiency and the life are further raised when the compound according to the invention is used as a positive hole charge transportation material compared with a usual positive hole charge transportation material.
The invention and its preferable embodiments are described.
1. An electro-luminescent element comprising an organic compound layer, wherein the organic compound layer contains a compound represented by Formula I or Formula V: 
xe2x80x83wherein R1 and R2 are each a substituent, and Ar is an aromatic hydrocarbon ring or an aromatic heterocyclic ring each of them may have a substituent, 
xe2x80x83wherein R11 through R16 and X1 through X9 are each a hydrogen atom or a substituent, they may be the same or different; and the sum of the steric parameters EsR1 through EsR16 of R11 through R16 respectively satisfies the following expression:
EsR11+EsR12+EsR13+EsR14+EsR15+EsR16xe2x89xa6xe2x88x922.0.
2. The organic electro-luminescent element of item 1, wherein the organic compound layers contains a compound represented by Formula I.
3. The organic electro-luminescent element of item 1, wherein the organic compound layers contains a compound represented by Formula V.
4. The organic electro-luminescent element of item 2, wherein the Ar in Formula I is a group represented by Formula II: 
xe2x80x83wherein one or more R3s are each a substituent and n1 is an integer of from 0 to 7.
5. The organic electro-luminescent element of item 4, wherein Ar in Formula I is a group represented by Formula III: 
xe2x80x83wherein one or more R4 and R5 are each a substituent, n2 is an integer of from 0 to 6, and n3 is an integer of from 0 to 7.
6. The electro-luminescent element of item 2 wherein the organic compound is a compound represented by Formula IV: 
xe2x80x83wherein at least one of R6, R7 and R8 is an alkyl group, a cycloalkyl group, an aryl group, a halogen atom, an alkoxy group, an aryloxy group or a heterocyclic group; and n4, n5 and n6 are each an integer of from 0 to 7.
7. The organic electro-luminescent element of item 3, wherein the organic compound is represented by 
xe2x80x83wherein R21 through R26, X21 through X26 and A1 through A6 are each a hydrogen atom or a substituent, they may be the same or different; and the sum of the steric parameters EsR21 through EsR26 of R21 through R26 satisfies the following expression:
EsR21+EsR22+EsR23+EsR24+EsR25+EsR26xe2x89xa6xe2x88x922.0.
8. The organic electro-luminescent element of item 1, wherein R1 and R2 are each an alkyl or alkoxy group or halogen atom, and Ar is a naphthyl, binaphthyl, quinolyl, iso-quinolyl, benzoxazolyl or benzimidazolyl group, wherein each of R1, R2 and Ar may have a substituent.
9. The organic electro-luminescent element of item 4, wherein R3 is halogen atom, an alkyl group, a cycloalkyl group, an aralkyl group, an aryl group, an alkoxy group, an aryloxy group, and a heterocyclic group, each of which may have a substituent.
10. The organic electro-luminescent element of item 5, wherein R4 and R5, which may be same or different, each represents a halogen atom, an alkyl group, a cycloalkyl group, an aralkyl group, an aryl group, an alkoxy group, an aryloxy group, a cyano group and a heterocyclic group, each of which may have a substituent.
11. The organic electro-luminescent element of item 6, wherein R6, R7 and R8 each represents a methyl or naphthyl group.
12. The organic electro-luminescent element of item 1, wherein organic compound layer is provided between a cathode and an anode.
13. A display apparatus comprising a plural number of organic electro-luminescent element of item 1 on a support.